The invention relates to improvements in friction clutches in general, and more particularly to improvements in friction clutches for use in the power trains of motor vehicles. Still more particularly, the invention relates to improvements in friction clutches of the type equipped with means for compensating for wear upon the friction surface of the pressure plate and/or counterpressure plate, upon the means for biasing the pressure plate against the adjacent friction linings of the clutch disc but at least upon the friction linings of the clutch disc. The wear upon the friction linings of the clutch disc is especially pronounced when the friction clutch is at least partially engaged, i.e., when the friction linings of the clutch disc are free to slide relative to the adjacent friction surfaces of the pressure plate and of the counterpressure plate. The latter can constitute a single flywheel or a composite flywheel which normally receives torque from the rotary output element of a prime mover, e.g., from the crankshaft or camshaft of the internal combustion engine in the power train of a motor vehicle.
The pressure plate in a friction clutch of the above outlined character is normally rotatable with, disposed in and movable within limits axially of the housing of the friction clutch. The housing is normally rotated by the output element of the prime mover, and the pressure plate is acted upon by the aforementioned biasing means which normally includes at least one diaphragm spring arranged to react against the rear wall of the housing or against an annuar seat on such rear wall and to urge the pressure plate axially toward the clutch disc.
The means for compensating for wear, at least upon the friction linings of the clutch disc, can comprise two annular arrays of complementary ramps which operate between the rear wall of the housing and the diaphragm spring (either directly or by way of the aforementioned seat) and means for turning one array of ramps relative to the ramps of the other array to an extent which is necessary to move the pressure plate and the diaphragm spring toward the counterpressure plate through a distance which is necessary to compensate for wear upon the friction linings alone or upon the friction linings and at least one additional part such as the friction surface of the pressure plate, the friction surface of the counterpressure plate, those surfaces of the diaphragm spring which come into contact with neighboring parts, and/or others. The purpose of adjustment or compensation for wear is to ensure that, when the friction clutch is engaged, the bias of the diaphragm spring upon the pressure plate remains at least substantially unchanged during the entire useful life of the friction clutch. In other words, the conicity of the diaphragm spring in the engaged condition of the friction clutch is to remain at least substantially unchanged, regardless of the extent of wear at least upon the friction linings of the clutch disc. By the same token, the force which is required to disengage such friction clutch, too, can remain at least substantially constant during the useful life of the friction clutch; this contributes significantly to convenience of operation or manipulation of the motor vehicle.
Automatically adjustable friction clutches which embody the aforediscussed wear compensation feature have been found to be highly useful in the power trains of motor vehicles and enjoy a widespread use. An advantage of such friction clutches is the convenience of engagement and disengagement during the entire useful life. In addition, such friction clutches contribute to a significant reduction of the maintenance and repair cost of the power train in a motor vehicle. Still further, it has been discovered that, even though the initial cost of a friction clutch with an automatic compensation for wear (especially upon the friction linings forming part of the clutch disc) is evidently higher than that of a standard friction clutch without a wear compensation feature, one can even achieve noticeable savings for the combined cost of the automatically adjustable friction clutch and the clutch engaging/disengaging means, e.g., by rendering it possible to dispose with a servo amplifier, by reducing the space requirements of the friction clutch, and/or by reducing the number of various versions of friction clutches and the engaging/disengaging means therefor.
Friction clutches with automated compensation for wear upon the friction linings of the clutch disc are disclosed, for example, in commonly owned published German patent applications Ser. Nos. 42 39 291, 43 06 505, 42 39 289, 195 24 827 and 197 07 785. The disclosures of all U.S. and foreign patents and patent applications identified in this specification by patent number, serial number and/or otherwise are to be interpreted as having been incorporated herein by reference. This applies also for the disclosure of our German priority patent application Ser. No. 198 11 937.2 filed Mar. 19, 1998.
Friction clutches of the type to which the present invention pertains are further disclosed in commonly owned U.S. Pat. No. 5,628,389 (which corresponds to the aforementioned commonly owned published German patent application Ser. No. 195 24 827) and in the corresponding published French patent application Ser. No. 2 723 992. In such friction clutches, a compensation for wear (particularly upon the friction linings of the clutch disc) necessitates an axial shifting of the diaphragm spring relative to the housing of the friction clutch.
In a conventional friction clutch, the magnitude of the clutch engaging force (F.sub.A) must be increased in response to increasing wear upon the friction linings of the clutch disc. The clutch engaging force need not be increased if the friction clutch is equipped with means to compensate for wear at least upon the friction linings of the clutch disc. In many instances, the wear compensating means is designed to compensate for wear upon certain additional parts of the friction clutch, such as the friction surface of the pressure plate and/or the friction surface of the counterpressure plate, the wear upon the diaphragm spring, the wear upon the parts of the seat for the diaphragm spring and/or others.
The friction linings of a clutch disc or clutch plate for use between the pressure plate and the counterpressure plate of a friction clutch can be mounted directly on the radially outermost portion of a washer-like carrier forming part of the clutch disc, or at opposite sides of a set of resilient segments which are carried by the aforementioned washer-like carrier of the clutch disc. Reference may be had to commonly owned U.S. Pat. No. 5,632,365.
Friction clutches wherein the means for compensating for wear upon the friction linings of the clutch disc operate between the rear wall and/or another part of the housing of the friction clutch and the diaphragm spring are disclosed, for example, in commonly owned U.S. Pat. No. 5,409,091 (granted to Wolfgang Reik et al.) and U.S. Pat. No. 5,450,934 (granted to Paul Maucher).